全文获取类型
收费全文 | 1648篇 |
免费 | 12篇 |
专业分类
1660篇 |
出版年
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 64篇 |
2012年 | 45篇 |
2011年 | 64篇 |
2010年 | 95篇 |
2009年 | 74篇 |
2008年 | 56篇 |
2007年 | 82篇 |
2006年 | 62篇 |
2005年 | 61篇 |
2004年 | 39篇 |
2003年 | 28篇 |
2002年 | 14篇 |
2001年 | 20篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1998年 | 40篇 |
1997年 | 62篇 |
1996年 | 74篇 |
1995年 | 40篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 38篇 |
1991年 | 33篇 |
1990年 | 36篇 |
1989年 | 37篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 25篇 |
1985年 | 27篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 26篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 18篇 |
1974年 | 11篇 |
1973年 | 18篇 |
1972年 | 21篇 |
1971年 | 33篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1959年 | 5篇 |
1952年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有1660条查询结果,搜索用时 15 毫秒
1.
2.
ABSTRACT. An actograph is described for recording the behaviour of small insects, by using a standing-wave radar system in an enclosed metal cabinet. Experiments show that the system produces an output frequency dependent only on the speed of movement of the subject. By filtering the signal electrically into components below and above 5 Hz, walking and flying of adult Musca domestica could be separately recorded. Each filter is followed by a level-comparator with hysteresis. Activity causing signal to cross the hysteresis-band is recorded as an event on a digital counter, and also integrated or summed to be displayed as a stepped-integral or bar-chart of total distance covered by the subject in each counting period. The energy-density of the radar can be kept very low, so that possible influence on the subject is minimal. The detector is remote from the box containing the subject, giving great flexibility in container design, so that the apparatus is ideally suited to the study of environmental factors. 相似文献
3.
THE TIMING OF DIVISION IN CHLAMYDOMONAS 总被引:3,自引:2,他引:1
4.
5.
6.
SUMMARY. 1. The organic geochemistry of Coniston Water, a low productivity lake, has been investigated.
2. The relative inputs of the various known sources to different compound classes suggest terrestrial higher plants as the major source of sedimentary organic matter.
3. Early lipid diagenesis, proceeding in the bottom sediments as a result of microbial activity, produces relatively rapid changes, with shorter chain and unsaturated compounds being preferentially degraded.
4. Free and bound (acid liberated) lipids exhibit significant differences in composition, related to their respective sources and stability towards degradation.
5. The lipid composition of an aquatic higher plant, growing in the margins of the lake, has been determined; comparison with the sedimentary lipids reveal it not to be a significant source. 相似文献
2. The relative inputs of the various known sources to different compound classes suggest terrestrial higher plants as the major source of sedimentary organic matter.
3. Early lipid diagenesis, proceeding in the bottom sediments as a result of microbial activity, produces relatively rapid changes, with shorter chain and unsaturated compounds being preferentially degraded.
4. Free and bound (acid liberated) lipids exhibit significant differences in composition, related to their respective sources and stability towards degradation.
5. The lipid composition of an aquatic higher plant, growing in the margins of the lake, has been determined; comparison with the sedimentary lipids reveal it not to be a significant source. 相似文献
7.
On blocking rules for the bootstrap with dependent data 总被引:9,自引:0,他引:9
We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton1/3, n1/4 and n1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically. 相似文献
8.
9.
LINDA M. McINNES IAN R. DADOUR MEREDITH E. STEWART WILLIAM G. F. DITCHAM PETER MAWSON PETER B. S. SPENCER 《Molecular ecology resources》2005,5(3):504-506
Microsatellite loci were isolated from Carnaby's black cockatoo (Calyptorhynchus latirostris: Aves), a highly valued, endangered, and endemic species of bird from Western Australia. This study describes three dinucleotide and one tetranucleotide microsatellite loci for which the primers produced clear and polymorphic amplification patterns with between two and nine alleles and moderate levels of variability. Two additional dinucleotide markers which were monomorphic in the Carnaby's cockatoo were able to amplify and were polymorphic in two other species of black cockatoo, greatly increasing the utility of these markers. 相似文献
10.
The Enigma of the Dinoflagellate Chromosome 总被引:3,自引:0,他引:3
PETER J. RIZZO 《The Journal of eukaryotic microbiology》1991,38(3):246-252